Cowboy Code Rewind
Tsk, tsk. He has forgotten the code already.
This is an issue we addressed in Chapter One of the Cowboy Code.
But for those who don't want to go back and read Chapter One, here's the deal:
You should not want or try to date your buddy's ex or your chick friend's ex guy, just 'cause there are too many fish in the sea to cast the net so close to home. If you're tempted by your buddy's or chick friend's ex just remember that when the friend and the ex were together, you always treated the ex as a sister or brother. Keep thinking of them that way and you won't be tempted to cross that line.
You should not want or try to date your buddy's ex or your chick friend's ex guy if their breakup was recent (I say under six months).
You should not want or try to date your buddy's ex or your chick friend's ex guy, if their breakup was recent and he/she still lives in the same city as you and your buddy/chick friend.
If an appropriate amount of time has passed and you "just happened" to fall for your buddy's/chick friend's ex, and you absolutely have to be with the ex, then do the right thing and tell your buddy/chick friend about your new romance. And tell 'em face to face. Don't be a coward and tell over the phone.
And (you may disagree with me on this one) if you tell your buddy/chick friend and they're still really bummed out over the breakup, you have a responsibility as a friend to not flaunt your new relationship with their ex. Keep it low key until the hard feelings have passed or until enough time has passed that you can say to your friend "Hey buddy, grow up. Get over it. You and I are old friends. You two didn't work out. It just so happens things did work out for us. Wish us well and get over it."
But seriously, if you really need a date look somewhere else. Why walk into unnecessary drama?